Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy
It is known that the addition of Cr to the Fe₃Al-based alloys leads to an improvement in their ductility and other properties. In a given work, dilatometric, differential scanning calorimetric (DSC) and internal friction tests are performed to study the ordering process in stoichiometric and oversto...
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| Zitieren: | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy / Z. Belamri, D. Hamana, I.S. Golovin, I.B. Chudakov // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 209-223. — Бібліогр.: 30 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860250134713991168 |
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| author | Belamri, Z. Hamana, D. Golovin, I.S. Chudakov, I.B. |
| author_facet | Belamri, Z. Hamana, D. Golovin, I.S. Chudakov, I.B. |
| citation_txt | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy / Z. Belamri, D. Hamana, I.S. Golovin, I.B. Chudakov // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 209-223. — Бібліогр.: 30 назв. — англ. |
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| description | It is known that the addition of Cr to the Fe₃Al-based alloys leads to an improvement in their ductility and other properties. In a given work, dilatometric, differential scanning calorimetric (DSC) and internal friction tests are performed to study the ordering process in stoichiometric and overstoichiometric Fe₃Al alloys with Cr addition at a constant heating rate from room temperature up to 1000°C. The results indicate that the addition of Cr slows the D0₃-type ordering process; this can be confirmed by obtained values of activation energy. Cr addition has also an effect on the mechanical properties of studied alloys annealed in D0₃-type order domain. The heights and broadening of three peaks (of X-, Zener-, and Snoek-type) can be changed at the presence of Cr. X-ray diffraction (XRD) and TEM studies are carried out at different temperatures chosen from the obtained DSC curves and affirmed that a rapid quenching just after heat treatment from highest temperature cannot suppress the formation of B2 ordered particles in overstoichiometric Fe₃Al alloys.
Відомо, що додавання Cr до стопів на основі Fe₃Al спричиняє поліпшення їх пластичности та інших властивостей. У даній статті виконано дилатометричні випробування та випробування методами диференційної сканівної калориметрії (ДСК) і внутрішнього тертя з метою вивчення процесу впорядкування в стехіометричних та надстехіометричних стопах Fe₃Al з додаванням Cr при сталій швидкості нагрівання від кімнатної температури до 1000°C. Додавання Cr сповільнює процес упорядкування за надструктурним типом D0₃, що підтверджується одержаними значеннями енергії активації. Додавання хрому впливає також на механічні властивості досліджених стопів, відпалених в області D0₃-порядку. Висоти та розширення трьох піків (Зінерового, Снукового та X-типу) можуть змінюватися в присутності Cr. Рентґенодифракційна аналіза та трансмісійна електронна мікроскопія, виконані за різних температур, обраних на підставі одержаних ДСК-кривих, підтвердили, що швидке гартування від самої високої температури зразу після теплового оброблення не може пригнітити формування впорядкованих частинок типу B2 у надстехіометричних стопах Fe₃Al.
Известно, что добавление Cr к сплавам на основе Fe₃Al приводит к улучшению их пластичности и других свойств. В данной статье выполнены дилатометрические испытания и испытания методами дифференциальной сканирующей калориметрии (ДСК) и внутреннего трения с целью изучения процесса упорядочения в стехиометрических и сверхстехиометрических сплавах Fe₃Al с добавлением Cr при постоянной скорости нагрева от комнатной температуры до 1000°C. Добавление Cr замедляет процесс упорядочения по сверхструктурному типу D0₃, что подтверждается полученными значениями энергии активации. Добавление хрома влияет также на механические свойства исследуемых сплавов, отжигаемых в области D0₃-порядка. Высоты и уширение трёх пиков (зинеровского, снуковского и X-типа) могут изменяться в присутствии Cr. Рентгенодифракционный анализ и просвечивающая электронная микроскопия, выполненные при различных температурах, выбранных на основании полученных ДСК-кривых, подтвердили, что быстрая закалка от самой высокой температуры сразу после тепловой обработки не может подавить формирование упорядоченных частиц типа B2 в сверхстехиометрических сплавах Fe₃Al.
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209
PACS numbers:61.72.Hh, 62.20.Qp,62.25.-g,62.40.+i,64.60.Cn,81.30.Hd, 81.70.Pg
Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry,
Heat Flow and Mechanical Spectroscopy
Z. Belamri, D. Hamana, I. S. Golovin*, and I. B. Chudakov**
Research Unit on Materials Science and Applications,
Mentouri University of Constantine,
Ain El Bey Road, 325,
25000 Constantine, Algeria
*National Research Technological University ‘MISiS’,
Leninskiy Ave., 4,
119049 Moscow, Russia
**State Research Center of Russian Federation
‘I. P. Bardin Central Research Institute for Ferrous Metallurgy’,
2nd
Baumanskaya Str., 9/23,
105005 Moscow, Russia
It is known that the addition of Cr to the Fe3Al-based alloys leads to an im-
provement in their ductility and other properties. In a given work, dilato-
metric, differential scanning calorimetric (DSC) and internal friction tests
are performed to study the ordering process in stoichiometric and over-
stoichiometric Fe3Al alloys with Cr addition at a constant heating rate from
room temperature up to 1000°C. The results indicate that the addition of Cr
slows the D03-type ordering process; this can be confirmed by obtained values
of activation energy. Cr addition has also an effect on the mechanical proper-
ties of studied alloys annealed in D03-type order domain. The heights and
broadening of three peaks (of X-, Zener-, and Snoek-type) can be changed at
the presence of Cr. X-ray diffraction (XRD) and TEM studies are carried out
at different temperatures chosen from the obtained DSC curves and affirmed
that a rapid quenching just after heat treatment from highest temperature
cannot suppress the formation of B2 ordered particles in overstoichiometric
Fe3Al alloys.
Відомо, що додавання Cr до стопів на основі Fe3Al спричиняє поліпшення
їх пластичности та інших властивостей. У даній статті виконано дилато-
метричні випробування та випробування методами диференційної скані-
вної калориметрії (ДСК) і внутрішнього тертя з метою вивчення процесу
впорядкування в стехіометричних та надстехіометричних стопах Fe3Al з
додаванням Cr при сталій швидкості нагрівання від кімнатної температу-
ри до 1000°C. Додавання Cr сповільнює процес упорядкування за над-
Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol.
2013, т. 35, № 2, сс. 209—223
Оттиски доступны непосредственно от издателя
Фотокопирование разрешено только
в соответствии с лицензией
© 2013 ИМФ (Институт металлофизики
им. Г. В. Курдюмова НАН Украины)
Напечатано в Украине.
210 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
структурним типом D03, що підтверджується одержаними значеннями
енергії активації. Додавання хрому впливає також на механічні власти-
вості досліджених стопів, відпалених в області D03-порядку. Висоти та
розширення трьох піків (Зінерового, Снукового та X-типу) можуть змі-
нюватися в присутності Cr. Рентґенодифракційна аналіза та трансмісійна
електронна мікроскопія, виконані за різних температур, обраних на підс-
таві одержаних ДСК-кривих, підтвердили, що швидке гартування від са-
мої високої температури зразу після теплового оброблення не може приг-
нітити формування впорядкованих частинок типу B2 у надстехіометрич-
них стопах Fe3Al.
Известно, что добавление Cr к сплавам на основе Fe3Al приводит к улуч-
шению их пластичности и других свойств. В данной статье выполнены
дилатометрические испытания и испытания методами дифференциаль-
ной сканирующей калориметрии (ДСК) и внутреннего трения с целью
изучения процесса упорядочения в стехиометрических и сверхстехиомет-
рических сплавах Fe3Al с добавлением Cr при постоянной скорости нагре-
ва от комнатной температуры до 1000°C. Добавление Cr замедляет про-
цесс упорядочения по сверхструктурному типу D03, что подтверждается
полученными значениями энергии активации. Добавление хрома влияет
также на механические свойства исследуемых сплавов, отжигаемых в об-
ласти D03-порядка. Высоты и уширение трёх пиков (зинеровского, снуко-
вского и X-типа) могут изменяться в присутствии Cr. Рентгенодифракци-
онный анализ и просвечивающая электронная микроскопия, выполнен-
ные при различных температурах, выбранных на основании полученных
ДСК-кривых, подтвердили, что быстрая закалка от самой высокой темпе-
ратуры сразу после тепловой обработки не может подавить формирование
упорядоченных частиц типа B2 в сверхстехиометрических сплавах Fe3Al.
Key words: intermetallics, ordering, phase transformation, dilatometry,
hardness measurement, internal friction.
(Received September 11, 2012)
1. INTRODUCTION
Properties of the Fe—Al alloys are low density, high melting temperature
and hardness, a good oxidation resistance coupled with a good resistance
to the fracture. They create a large prospect for the Fe—Al alloys indus-
trial application, for example as components of the machines used at
high temperature, in corrosive environment (Refs. 6—9 cited by [1—3]) or
as high damping alloys [4—6]. However, these materials have a low duc-
tility at room and elevated temperature [7]. The ductility and corrosion
resistance can be improved by the addition of a third element, for ex-
ample chromium. The field of application of ternary Fe—Al—Cr alloys is
very vast, primarily as substrate for a catalyst applied in the catalytic
converters and as filter in automobiles [8].
An important feature of this system is the high solubility of both Al
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 211
and Cr in b.c.c. iron. The Cr atoms occupy most probably the 4b or 8c
positions (Fig. 1) with some preference of next nearest neighbour Al
positions [9]. The dissociation energy for Cr—Al pairs (W(Cr −Al) =
= 0.6960 eV) that is lower than for Fe−Al pairs (W(Fe−Al) = 0.7457 eV) is
responsible for the mentioned decrease of the antiphase boundary (APB)
energy. The density of vacancies in Fe—25Al—(15—25)Cr alloys quenched
from 1273 K was detected to be about cV ≈ 3⋅10
−5
at
−1, which is three
times lower than that in Fe—25Al (cV ≈ 10
−4
at
−1
[10]) but higher than it is
in Fe−Si−Al alloys.
Recent studies show the utility of the addition of Cr in Fe—Al based
alloys; the Fe—(25—28)Al* alloys are often alloyed with 3—5% Cr to in-
crease their ductility and their workability (Ref. 1 cited by [11]). Sikka
et al. [12] observed that ductility at room temperature in Fe—28Al al-
loy was increased by the addition of 5% Cr. McKamey et al. [13] show
that the addition of 6% Cr leads to the increase in ductility at low tem-
perature from 4% to 8—10% approximately. Since the dissociation en-
ergy W(Cr—Al) is lower than W(Fe—Al), it results in an improvement of the
intrinsic ductility of Fe3Al due to the decrease in the energy of the an-
tiphase boundary, increasing the mobility and the slip of dislocations
*All compositions in this paper are given in atomic percents.
Fig. 1. Lattice structure in Fe3Al: 4a (Al) positions–full circles, 4b (Fe)–grey
circles, and 8c (Fe)–open circles.
212 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
(Ref. 28 cited by [11] and [14]). The presence of Cr in Fe—28Al—3Cr al-
loy improves the pitting corrosion resistance by the increase of the pit-
ting potential of the alloy [15].
Chromium does not have a significant effect on the value of the transition
temperature from D03 to B2 (T0) phases and slightly increases the transition
interval A2 → D03 of quenched (Fe,Cr)3Al alloys according to the differential
scanning calorimetric (DSC) data showed in this work. Hamana et al. [16]
showed that the ternary element (addition of 2% Cr and 5% Cr in Fe—28Al
alloy) stabilizes the B2 ordered phase and slows the B2 → D03 transition.
The purpose of this paper is to study the order—disorder transition in
Fe—Al—Cr alloys using differential scanning calorimetry, dilatometry, and
related internal friction effects by mechanical spectroscopy technique.
2. MATERIALS AND EXPERIMENTAL METHODS
The alloys used in this work have the following compositions: Fe—25Al—
25Cr, Fe—25Al—9Cr, Fe—28Al—4Cr and Fe—27Al—2Cr. Before charac-
terization, the samples were homogenized for one hour at 1000°C and
water quenched. The samples have a cylindrical shape for the dilato-
metric analysis (12×3 mm), and for the DSC analysis (5×5 mm).
For tests a DSC 131 SETARAM and DI24 ADAMEL LHOMARGY
dilatometer connected to a computer respectively were used; suitable
software allows analysing and determining the critical points on the
recorded curves. The internal friction (IF), i.e. damping Q
−1, is meas-
ured as a function of temperature at vibrating reed setup at resonance
frequency of one side clamped sample with ε0 ≈ 10
−5.
The microhardness is measured with a load of 3 N using a ZWICK
apparatus connected to the computer with adapted software provided
the values of HV automatically.
To identify the type of phases appearing in the studied alloys, Sie-
mens D8 Advance diffractometer is used. The recorded XRD patterns
were obtained with Cu anticathode (I = 40 mA, V = 40 kV). The trans-
mission electron microscopy (Philips CM12) is used for the characteri-
zation of the alloys.
3. RESULTS AND DISCUSSIONS
Specimens were characterized at heating and cooling by DSC, dilatom-
etry and internal friction measurements. X-ray diffraction (XRD) and
TEM studies were performed after chosen heat treatment regimes.
3.1. Differential Scanning Calorimetric Study
The DSC curves obtained with heating rate of 10°C/min (Figs. 2, a—d) of
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 213
homogenised 1 h at 1000°C and water quenched Fe—25Al—25Cr, Fe—
25Al—9Cr, Fe—28Al—4Cr, Fe—27Al—2Cr alloys, respectively, demon-
strate the following effects.
An exothermic peak linked to the formation of the ordered phase
from α partial disordered state. Nevertheless, we can detect some or-
der by XRD after water quenching of these alloys (see below in
Figs. 5, a—d). TEM micrograph of water quenched Fe—26Al sample [17]
shows antiphase boundaries with large B2 domain and very fine D03
domains can be distinguished. According to Allen (Ref. 9 cited by
[18]), this transition undergoes the following sequence: α → B2 →
→ D03 in overstoichiometric Fe—Al alloys. B2 order is also found in
Fe—25Al—25Cr after quenching from 1250 K (Fig. 3, a). Therefore,
the rapid quenching of studied alloys after heat treatment at high
temperature cannot suppress the formation of the B2 ordered parti-
cles. D03 domains were observed by TEM in Fe—25Al—9Cr, while B2
and D03 domains are observed in Fe—25Al—25Cr composition after
annealing at 748 K and quenching. In TEM micrographs of these two
alloys (see Figs. 3, b, c), fine D03 domains for Fe—25Al—25Cr (do-
mains are fine because the temperature is rather close to the D03 to
Fig. 2. DSC curves of the homogenised 1 h at 1000°C and water quenched
(heating rate = 10°C/min): Fe—25Al—25Cr (a), Fe—25Al—9Cr (b), Fe—28Al—
4Cr (c), Fe—27Al—2Cr (d) alloys.
214 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
B2 transition) and coarse D03 domains for Fe—25Al—9Cr are present-
ed. Cooling rate of the Fe—25Al—25Cr alloy has a great influence on
the type of order: B2 or D03 [19].
An endothermic peak caused by the decrease in the order of the D03
ordered phase and the formation of the B2 ordered phase.
An exothermic peak is observed during cooling, which corresponds
to the B2 → D03 transition on all DSC curves; however, on the DSC
curve of Fe—25Al—25Cr this peak is broad and it is difficult to specify
temperature: high amount of Cr slows the transition.
It should be noted that the effects observed on the DSC curves in
studied Fe—Al—Cr alloys are rather similar to those in binary Fe—Al al-
loys [18]. The influence of composition of studied alloys on order—
disorder transition temperatures is summarized in Table 1.
Fig. 3. TEM micrographs of Fe—25Al—25Cr alloy homogenized at 1000°C and
water quenched (a), Fe—25Al—25Cr sample water quenched from 1000°C then
annealing 48 h at 475°C (b), Fe—25Al—9Cr sample water quenched from
1000°C then annealing 48 h at 475°C (c).
TABLE 1. Nominal composition, phase transitions temperatures of studied
alloys according to the DSC and dilatometric analysis (heating/cooling rate
10°C/min).
Nominal
composition
DSC (heating + cooling) Dilatometry (heating)
α + D03 → D03 D03 → B2 B2 → D03 α + D03 → D03 D03 → B2
Fe—25Al—25Cr 329°C 527°C * 327°C 546°C
Fe—25Al—9Cr 297°C 548°C 534°C 255°C 550°C
Fe—28Al—4Cr 315°C 540°C 522°C 260°C 542°C
Fe—27Al—2Cr 288°C 539°C 521°C 247°C 538°C
* It is impossible to specify temperature.
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 215
3.2. Dilatometric Study
Dilatometric curves of the homogenised 1 h at 1000°C and water
quenched Fe—25Al—25Cr, Fe—25Al—9Cr, Fe—28Al—4Cr and Fe—27Al—
2Cr samples, obtained with a heating rate of 10°C/min (Figs. 4, a—d)
respectively, show an important anomaly and the derivative heating
curves show the following effects: contraction caused by the formation
of the D03 ordered phase starting from the α disordered phase; expan-
sion caused by the decrease in the order of D03 ordered phase and the
formation of the B2 ordered phase.
In general, the dilatometry data confirm the heat flow data. Some
insignificant quantitative differences are caused by different sensitiv-
ity of these methods.
3.3. XRD Study
XRD analysis is carried out in order to confirm the nature of the phas-
es responsible for the appearance of the effects at DSC and dilatometric
curves during heating. All samples were homogenised 1 h at 1000°C,
and then heated up to the maximum temperatures of DSC peaks and
water quenched. The XRD patterns of the homogenized and water
Fig. 4. Dilatometric heating curves of the homogenised 1 h at 1000°C and wa-
ter quenched (heating rate = 10°C/min): Fe—25Al—25Cr (a), Fe—25Al—9Cr (b),
Fe—28Al—4Cr (c), Fe—27Al—2Cr (d) alloys; solid line–derivative heating
curve, dotted line–heating.
216 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
quenched alloys show the peaks of α disordered phase with small peaks
corresponding to the B2 ordered phase (Figs. 5, a—d). Table 2 summa-
rises the obtained results of XRD analysis of each alloy.
3.4. Determination of the Activation Energy of Ordering
Starink (Eq. (1), [20]), Kissinger (Eq. (2), [21]), and Ozawa (Eq. (3),
[22]) methods are used to estimate activation energy of the D03 order-
ing process in the studied alloys. The heat flow (DSC) measurements
are carried out at four different heating rates: 10, 15, 20 and
25°C/min. The variations of the temperature of the maximum of the
first exothermic peaks (Tm) with a heating rate β:
1mact
92.1
m )/(0008.1)/ln( CRTET +−=β , (1)
Fig. 5. XRD patterns of Fe—25Al—Cr alloys after homogenised 1 h at 1000°C
and water quenched then heating up to deferent temperatures indicated on
each figure.
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 217
2mact
2
m /)/ln( CRTET +−=β , (2)
3mact )/(0516.1ln CRTE +−=β . (3)
Figures 6, a—d show the superposition of DSC curves of studied alloys,
where the exothermic peak related to the formation of D03 ordered phase
appears; they reveal that the increase of the heating rate β leads to the
shift of the maximum of the exothermic peaks toward high temperatures.
The activation energy of ordering process of the D03 phase (Table 3) in
the studied alloys is deduced from the different methods presented in
Figs. 7, a—d. All three methods give almost the same values for each alloy.
The value of the activation energy rises with the increase of the Cr
content in Fe3Al compound, which means that the ordering process of
D03 ordered phase formation in the alloy with higher Cr amount re-
quires more energy. The diffusion coefficient is governed by the expo-
nential law [23]:
)/exp( act0 RTEDD −= . (4)
If the value of the Eact is high, the diffusion is slow; thus, the addition
of chromium slows the ordering process. It is in agreement with the
results obtained by the dilatometric and differential calorimetric anal-
ysis.
3.5. Temperature Dependent Internal Friction
Internal friction spectra of binary Fe—Al alloys have been studied by
several researchers [24]: at least three thermally activated peaks were
recorded at elevated temperatures: the carbon Snoek (S), Zener (Z) re-
TABLE 2. The different phases obtained by XRD in studied alloys after heat
treatments.
Alloy Water quenched after heating up to Structure of phases
Fe—25Al—25Cr
329°C A2 + D03
527°C D03 + B2
Fe—25Al—9Cr
297°C A2 + D03
548°C D03 + B2
Fe—28Al—4Cr
315°C A2 + D03
540°C D03 + B2
Fe—27Al—2Cr
288°C A2 + D03
539°C D03 + B2
218 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
laxations and less explained (X) effect; they are caused by the presence
of structural vacancies and carbon atoms in alloys. Chromium is a car-
bide-forming element both in iron and in Fe—Al-based alloys. Calcula-
tions [25] have demonstrated that the C−Cr ‘chemical’ plus ‘elastic’
interatomic interaction in iron takes place up to the fifth coordination
shell, however, some interstitial carbon remains in solid solution after
water quenching [26]; that results in the appearance of the so-called
Snoek-type peak [10] (denoted as the S peak in Fig. 8).
If the Al content exceeds the Cr content, the Snoek-type peak shifts
to higher temperatures than those of Fe—31Al, which is caused by the
additional C−Cr interaction [27], while the Snoek-type peak height de-
crease is caused by the decrease in the carbon amount in solid solution.
The X peak also recorded in Fig. 8 was interpreted earlier [28, 29] as a
relaxation peak caused by C-vacancy reorientation in the applied stress
field. For the case of a fixed Al content (≅ 25 at.%) and Cr substituting
Fe, all above-mentioned tendencies can also be seen but the relative
Fig. 6. Parts of DSC curves corresponding to the D03 ordered phase formation
in homogenised 1 h at 1000°C, water quenched then heated with various rates
Fe—25Al—25Cr (a), Fe—25Al—9Cr (b), Fe—28Al—4Cr (c), Fe—27Al—2Cr (d) al-
loys.
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 219
changes are different (see Fig. 8).
The high Cr addition has a remarkable effect on the damping capaci-
ty of Fe3Al based alloys. Below 450°C (Fig. 8), progressive decrease of
Fig. 7. Starink’s plot to obtain the activation energy values of the D03 order-
ing process in: Fe—25Al—25Cr (a), Fe—25Al—9Cr (b), Fe—28Al—4Cr (c), Fe—
27Al—2Cr (d) alloys.
TABLE 3. Activation energy values of ordering process of the D03 ordered
phase formed during heating in homogenised 1 hour at 1000°C and water
quenched samples, estimated by three methods.
Alloy
Activation energy Eact, eV
Methods
Starink’s Kissinger’s Ozawa’s
Fe—25Al—25Cr 1.31 ± 0.19 1.31 ± 0.19 1.34 ± 0.18
Fe—25Al—9Cr 1.25 ± 0.23 1.25 ± 0.23 1.28 ± 0.22
Fe—28Al—4Cr 1.10 ± 0.11 1.09 ± 0.11 1.14 ± 0.11
Fe—27Al—2Cr 1.04 ± 0.17 1.04 ± 0.17 1.08 ± 0.16
220 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
the heights of S and X peaks is observed with the increase of Cr
amount, until their disappearance with addition of 25 at.% Cr.
The decrease in the Snoek-type and X peaks heights is probably caused
by the trapping of carbon atoms in chromium carbides, while a shift of
the Snoek-type peak to higher temperature is the result of the C−Cr in-
teraction in solid solution. The Snoek-type and X peaks can hardly be dis-
tinguished in some cases: only by stepwise Cr adding into Fe−Al.
The Zener relaxation peak–reorientation of pairs of substitute at-
oms under applied periodic stress–is slightly broadened and shifted to
higher temperatures as compared to binary Fe—Al alloys. The Al—Cr
and Cr—Cr interactions imply a broadened Zener peak at higher tem-
perature as compared to binary Fe—26Al, because the effects of Al and
Cr pairs are superposed (Fig. 8). No clear peaks were recorded in Fe—
25Al—25Cr alloys at the position that corresponds to the Zener peak in
the binary Fe—25Al composition; may be the Zener peak will appear
around or above 600°C, while the Snoek-type peak disappears in this
alloy because of high Cr amount.
3.6. Effect of Chromium on the Microhardness of Studied Alloys
Several theoretical and experimental works show that the mechanical
properties of Fe—Al alloys can be improved by the addition of chromi-
um. According to the obtained results of the microhardness measure-
ments for all studied alloys homogenised 1 h at 1000°C, water
quenched and then annealed at 300°C (temperature of formation of D03
Fig. 8. Q
−1(T) in homogenised and water quenched Fe—26Al and Fe—25Al—Cr
alloys for 1—2 Hz.
STUDY OF ORDERING IN Fe—25%Al—Cr ALLOYS 221
ordered phase) for various times, the formation of this phase leads to
the increase in the microhardness (Figs. 9, a—d).
The increase in microhardness with the increase in annealing time
takes place until a certain point: 60 min for Fe—25Al—25Cr alloy,
20 min for Fe—25Al—9Cr alloy, 15 min for Fe—28Al—4Cr alloy and
10 min for Fe—27Al—2Cr alloy; then hardness decreases. Increase in
hardness can be explained by the increase in order degree and, conse-
quently, by increase in the volume fraction of the D03 antiphase do-
main until the complete transformation of the α disordered phase to
the D03 ordered phase.
Beauchamp et al. (Ref. 2 cited by [30]) show that annealing at temper-
atures close to the critical temperature (formation of the D03 ordered
phase) reduced the energy of the antiphase boundaries with their sepa-
ration by approximately two, three or five atomic plains. The reduction
in the energy of these boundaries implies an increase in mobility of dis-
locations and leads to a better ductility (Ref. 1—5 cited by [17]). The de-
crease in the microhardness is caused by the coalescence of some anti-
phase boundaries [18]. The comparison between the microhardness
values of studied alloys shows that the maximum value is reached fast-
er in the alloy with slight Cr addition; this difference can be explained
by the effect of the chromium addition that slows the process of coales-
Fig. 9. Variation of the microhardness as a function of annealing time at
300°C for: Fe—25Al—25Cr (a), Fe—25Al—9Cr (b), Fe—28Al—4Cr (c), Fe—27Al—
2Cr (d) alloys.
222 Z. BELAMRI, D. HAMANA, I. S. GOLOVIN, I. B. CHUDAKOV
cence of the antiphase boundaries [18].
4. SUMMARY
The advanced properties of the Fe—Al alloys create a wide prospect for
their industrial applications. However, these materials present a poor
ductility at ambient temperature, which can be improved by the addi-
tion of the third element. Chromium is the favourable element for this
improvement. In this paper, we studied the effect of this element on
the order—disorder transitions in different ternary Fe—Al—Cr alloys.
Dilatometric and DSC studies show the different transitions exist-
ing in different studied Fe—Al—Cr alloys, and show that the addition of
Cr in Fe3Al compound slows the D03 ordering. This is additionally con-
firmed by the obtained values of activation energy of the ordering pro-
cess of the D03 ordered phase formed in studied alloys. Starink’s meth-
od permits to estimate the value of this energy in different studies al-
loys, and shows that the ordering process of D03 ordered phase requires
more energy in Fe3Al—Cr alloys with higher Cr amount (see Table 3).
XRD and TEM studies show that water quenching from high tempera-
ture cannot suppress the formation of B2 ordered particles in over-
stoichiometric Fe3Al alloys.
Annealing at temperature close to the temperature of D03 ordered
phase formation leads to an increase of the microhardness, which can
be explained by the increase of the fraction of the D03 antiphase do-
main boundaries until the complete formation of D03 ordered phase.
The maximum value of this microhardness is reached faster with lower
Cr addition than in the alloy with high percentage of Cr; thus, Cr addi-
tion slows the process of coalescence of antiphase boundaries.
Chromium has also an effect on the anelastic relaxation in these al-
loys; it leads to the decrease of the heights of the Snoek-type peak and
the peak at higher temperature that is tentatively explained by vacan-
cies and carbon complexes. The Snoek- and Zener-type peaks shift to
higher temperatures with increase in Cr content in alloys. A broaden-
ing of the Zener peak in presence of Cr can be explained by contribution
to Zener relaxation not only by Al—Al, but also by Cr—Cr and Al—Cr at-
om pairs.
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| id | nasplib_isofts_kiev_ua-123456789-104077 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1024-1809 |
| language | English |
| last_indexed | 2025-12-07T18:42:07Z |
| publishDate | 2013 |
| publisher | Інститут металофізики ім. Г.В. Курдюмова НАН України |
| record_format | dspace |
| spelling | Belamri, Z. Hamana, D. Golovin, I.S. Chudakov, I.B. 2016-07-01T09:13:37Z 2016-07-01T09:13:37Z 2013 Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy / Z. Belamri, D. Hamana, I.S. Golovin, I.B. Chudakov // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 209-223. — Бібліогр.: 30 назв. — англ. 1024-1809 PACS numbers:61.72.Hh, 62.20.Qp,62.25.-g,62.40.+i,64.60.Cn,81.30.Hd, 81.70.Pg https://nasplib.isofts.kiev.ua/handle/123456789/104077 It is known that the addition of Cr to the Fe₃Al-based alloys leads to an improvement in their ductility and other properties. In a given work, dilatometric, differential scanning calorimetric (DSC) and internal friction tests are performed to study the ordering process in stoichiometric and overstoichiometric Fe₃Al alloys with Cr addition at a constant heating rate from room temperature up to 1000°C. The results indicate that the addition of Cr slows the D0₃-type ordering process; this can be confirmed by obtained values of activation energy. Cr addition has also an effect on the mechanical properties of studied alloys annealed in D0₃-type order domain. The heights and broadening of three peaks (of X-, Zener-, and Snoek-type) can be changed at the presence of Cr. X-ray diffraction (XRD) and TEM studies are carried out at different temperatures chosen from the obtained DSC curves and affirmed that a rapid quenching just after heat treatment from highest temperature cannot suppress the formation of B2 ordered particles in overstoichiometric Fe₃Al alloys. Відомо, що додавання Cr до стопів на основі Fe₃Al спричиняє поліпшення їх пластичности та інших властивостей. У даній статті виконано дилатометричні випробування та випробування методами диференційної сканівної калориметрії (ДСК) і внутрішнього тертя з метою вивчення процесу впорядкування в стехіометричних та надстехіометричних стопах Fe₃Al з додаванням Cr при сталій швидкості нагрівання від кімнатної температури до 1000°C. Додавання Cr сповільнює процес упорядкування за надструктурним типом D0₃, що підтверджується одержаними значеннями енергії активації. Додавання хрому впливає також на механічні властивості досліджених стопів, відпалених в області D0₃-порядку. Висоти та розширення трьох піків (Зінерового, Снукового та X-типу) можуть змінюватися в присутності Cr. Рентґенодифракційна аналіза та трансмісійна електронна мікроскопія, виконані за різних температур, обраних на підставі одержаних ДСК-кривих, підтвердили, що швидке гартування від самої високої температури зразу після теплового оброблення не може пригнітити формування впорядкованих частинок типу B2 у надстехіометричних стопах Fe₃Al. Известно, что добавление Cr к сплавам на основе Fe₃Al приводит к улучшению их пластичности и других свойств. В данной статье выполнены дилатометрические испытания и испытания методами дифференциальной сканирующей калориметрии (ДСК) и внутреннего трения с целью изучения процесса упорядочения в стехиометрических и сверхстехиометрических сплавах Fe₃Al с добавлением Cr при постоянной скорости нагрева от комнатной температуры до 1000°C. Добавление Cr замедляет процесс упорядочения по сверхструктурному типу D0₃, что подтверждается полученными значениями энергии активации. Добавление хрома влияет также на механические свойства исследуемых сплавов, отжигаемых в области D0₃-порядка. Высоты и уширение трёх пиков (зинеровского, снуковского и X-типа) могут изменяться в присутствии Cr. Рентгенодифракционный анализ и просвечивающая электронная микроскопия, выполненные при различных температурах, выбранных на основании полученных ДСК-кривых, подтвердили, что быстрая закалка от самой высокой температуры сразу после тепловой обработки не может подавить формирование упорядоченных частиц типа B2 в сверхстехиометрических сплавах Fe₃Al. en Інститут металофізики ім. Г.В. Курдюмова НАН України Металлофизика и новейшие технологии Дефекты кристаллической решётки Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy Исследование упорядочения в сплавах Fe—25%Al—Cr с помощью дилатометрии, калориметрии теплового потока и механической спектроскопии Article published earlier |
| spellingShingle | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy Belamri, Z. Hamana, D. Golovin, I.S. Chudakov, I.B. Дефекты кристаллической решётки |
| title | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy |
| title_alt | Исследование упорядочения в сплавах Fe—25%Al—Cr с помощью дилатометрии, калориметрии теплового потока и механической спектроскопии |
| title_full | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy |
| title_fullStr | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy |
| title_full_unstemmed | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy |
| title_short | Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy |
| title_sort | study of ordering in fe—25%al—cr alloys by dilatometry, heat flow and mechanical spectroscopy |
| topic | Дефекты кристаллической решётки |
| topic_facet | Дефекты кристаллической решётки |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/104077 |
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